This invention relates to a fastener for securing two parts in spaced relation such as a sheet metal roof panel to a roof frame with a layer of insulation between the panel and the frame. The fastener includes an elongated shank with a tip at one end and a driving head at the other and the shank is inserted tip first through a hole, which may be either preformed in the panel or drilled by the tip, and is driven through the insulation layer. A thread formed on the shank adjacent the tip is driven into the frame to draw the head down. A washer on the shank beneath the head is compressed between the head and the panel to provide a seal around the shank at the hole in the panel. Prior fasteners of this type have presented a number of drawbacks among which are that the fastener may easily be overdriven, there is difficulty in obtaining and keeping a good seal between the washer and the plate, and the panel is readily subject to dimpling when exposed to external forces such as roof traffic.